1. Field of the Invention
The present invention generally relates to an apparatus and method for decontamination of soil and, more specifically, to an apparatus and method for relatively rapid, on-site soil decontamination in a confined area without significant toxic off-gassing.
2. Description of the Prior Art
In the recent few decades contaminated soil has become a serious concern. A great portion of the contaminated soil is tainted by fuel hydrocarbons or heavy metals. In response to this concern, both Federal and State governments has promulgated strict standards for clean soil and air. Therefore, upon discovery of contaminated soil a clean-up procedure must be employed or the responsible parties will face at least financial penalties.
Fuel hydrocarbons from gasoline or motor oil constitute a significant portion of the soil pollution problem. Gasoline leaking from service stations, municipal and institutional fuel storage tanks are, unfortunately, a regular discovery. Although the exact scope of the problem is not presently known, it is significant, and several States have mandated underground storage tank monitoring programs. Unlined gasoline tanks or containers have an extremely limited life and may start leaking after only five years of use and can not be expected to remain leak-free for any more than ten years. It has been estimated that more than 2400 leaking underground fuel storage tanks are located in California alone.
In response to this large scale soil contamination, various methods have been introduced in an effort to render a contaminated site usable and safe. However, the methods of the past are replete with significant drawbacks and high costs. The most common systems of the past include aeration, biodegradation, air-stripping, incineration, and removal of the contaminated soil to a Class One dump site.
Aeration is a technique whereby contaminated soil is spread in thin layers over an open area. When solar rays contact the soil, a partial oxidation of the fuel hydrocarbons results but toxins are released into the atmosphere. Due to this undesired release of pollutants, governmental standards require that only a limited amount of soil may be treated in a certain time structure. Therefore, simple aeration of only 500 cubic yards of soil with contaminate levels of 2,300 p.p.m. total fuel hydrocarbon would take approximately six years to complete under the current guidelines. Obviously, aeration is costly and renders the site useless until the soil is decontaminated.
A more rapid method of clean-up is the technique of removal of the contaminated soil to a Class One landfill. Like aeration, depositing the tainted soil in a landfill creates a significant introduction of pollutants into the atmosphere. Although the removal technique results in a clean site in a relatively short time, the costs and exposures associated therewith are high. Typically, soil transportation and disposal costs are currently between $250 and $380 per cubic yard, and additional costs are incurred if replacement soil is required. Also, the transportation of tainted soil creates an exposure to potential liability for any in route mishap or improper disposal.
Airstripping includes boring numerous holes into the contaminated soil and lowering perforated casings therein. The perforated casings are centrally connected with an air flow source whereby air is drawn around the decontaminated earth and pumped through an air filter system designed to trap the now airborne pollutants. Airstripping is only effective in sand or loam based soils because of the required air movement, and usually takes from five to fifteen years to complete which renders the site useless for that time. Additionally, the central air filter must be changed regularly or the system will deposit harmful pollutants into the atmospheric environment. Flooding of an airstripping system may create a worse problem than originally existed because the flood water is passed through the contaminated soil and may percolate down into the water table and pollute water supplies.
Biodegradation has also been employed as a technique to clean contaminated soil. Living organisms which digest or otherwise eliminate fuel hydrocarbons are introduced into the toxic soil. Over a lengthy period of time, these organisms may render the soil useful again. However, biodegradation does not solve the problem of rendering the site useless for an extended time period, nor is the total effect of the organisms on the ecosystems of the site a known factor. Further, biodegradation should not be used above oil fields because the organisms will continue to feed on the oil and thereby reduce the amount of oil reserves in the field. This is a serious drawback considering that a large percentage of the areas where soil contamination occurs are proximately located with oil fields.
Incineration treatment involves high temperature burning of contaminated soil. However, this method has yet to be proven effective, or governmentally approved, largely due to the offgassing of dioxins which are classified as hazardous and/or toxic.
None of the past systems effectively eliminate the problems and high costs associated with site clean-up, namely, air pollution, time restrictions, transportation and disposal costs and exposure, and rendering the site useless. Therefore, the subject apparatus and method fill an obvious need in the industry by eliminating these problems and high costs.